The invention relates to the technical fields of equipment for an excavator having buckets, cups or other receptacles capable of scraping or grabbing materials or the like with a view to their removal from a given place to other operating sites by means of an excavator.
It is well know, according to prior art, how to fit, on buckets or similar receptacles of an excavation engineering plant, shaped adapter tips which can be fitted with removable teeth having a matching profile. These teeth are in direct contact with the materials to be grabbed or scraped and are consequently subject to rapid wear due to stresses during use. The shaped adapter tips on buckets or receptacles are male parts joined to the lip of the preshaped bucket or receptacle and are produced as a separately mounted or one-piece part during formation of the bucket or receptacle.
Teeth that are separately mounted are female parts which have shapes which match the profiles of the adapter tip or tips and fit over them.
The need to change teeth as they wear requires a join between said wearing parts or teeth and the corresponding adapter tip. This joint is, according to the prior technique, made available by very many manufacturers in the form of a wedge-shaped key that can be of metal or hybrid construction and provide flexibility through a flexible material.
All the available systems according to the prior art have one feature in common: they exhibit and ensure a balance in the strength of the separately mounted tooth and the corresponding adapter tip. In fact, given the stresses during use, there must be a solid, constant connection between the tooth and the adapter tip which withstands the thrust and backward stresses encountered during the forces exerted. As shown diagrammatically in FIG. 1, the joint between the two parts is such that there must be a forward support area and rear backrest areas in the joint obtained between the tooth and the adapter tip.
Thus, according to the prior art, in a first embodiment, a monolithic key is used which fits into openings made on the adapter tip and on the corresponding tooth. This layout is shown in FIGS. 2 and 3. This layout is, however, difficult to achieve because it requires absolutely geometrically accurate positioning of the tooth with respect to the adapter, failing which the key, if its working faces are parallel, may not be able to enter into its recess or may not provide the desired tightening. In order to overcome this drawback, there have been suggestions to make the end of the base of the key with a bevel that provides a wedge affect. Nevertheless, its position when it is driven home remains random and sometimes the key may partially protrude on one side or the other, thus obstructing assembly. In addition, in this embodiment, holding of the key is not ensured and is not long-lasting and any unintentional shock at the thinner end of the key may cause it to protrude or come loose from its recess, thus making joining of the tooth to the adapter tip in question ineffective.
In order to overcome this drawback, a thinner end of the key has been suggested, as shown in FIG. 3, which can be folded over in order to prevent it from coming loose and, in another embodiment as shown in FIG. 4, the use of a cylindrical key with a retaining collar of the circlip type which makes it necessary to form a recess in the adapter tip or the use of a metal or rubber end retaining cap shown in FIG. 5 have been suggested. A multi-key system shown in FIG. 6 is also known which allows locking by a wedge effect due to opposite sloping surfaces.
In all these implementations, in order for the keying to remain effective in service if it is mechanical and direct with a monolithic key, the latter must be force fitted thus causing misshaping of the areas that receive the tooth with possible deformation of the key.
According to other solutions according to the prior art, mechanical keying by an elastic key has been suggested. This joining system makes it possible to simultaneously secure the tooth and retain the key. In this application the latitude given by the various devices is relatively small and does not make it possible to disregard the need for absolute geometrical accuracy in the positions of the tooth and of the adapter tip. In order to illustrate this layout, FIGS. 7 and 8 show metal keys which are elastic and have a curved shape which tends to deform when the key is fitted in the desired joint. These keys can be of the split pin type or be of solid cross-section. Alternatively, the central part of the keys can be fitted with a spring ring.
According to other possibilities of the prior art, keying comprising a rubber element that is either integrated in a sandwich structure (FIG. 9a) or independent (FIG. 9b) in combination with a key has been suggested. In this latter implementation, the rubber block comprises inserts and is made with alternating valleys and peaks spaced apart and positioned opposite and along the key in question so that they fit into matching valleys and peak shapes arranged on the key. Joining is obtained by assembling the two parts after previously inserting the rubber block and then forcing in the key. In this implementation the rubber block previously placed in its recess in the adapter must be accurately positioned with respect to the tooth and the key; it must be possible to insert the key by moving apart the peaks on the rubber block which must then spring back into the matching hollows in the key when the latter is in position. If tightening is excessive, the key cannot enter and may damage the rubber block by tearing it. If tightening is insufficient, the key goes in easily but there is no assurance that it will be secured in service.
All the known layouts according to the prior art show that there are a certain number of significant drawbacks such as difficulties in fitting and removing by force, poor gripping in service and loss of keys and teeth, movement of teeth on adapters which causes wear of the tip which worsens gradually as teeth are changed and, through the play thus created, contributes to their breakage.
In addition, connections with worn adapters are unreliable because the connecting elements, keys and rubber blocks of predetermined shapes and dimensions in order to conform with first fitting, no longer match them. Keys having special compensated shapes sometimes have to be used and this makes conditions of use considerably more complicated.
In every case absolute geometrical accuracy is required for the position of the tooth with respect to the adapter so that alignments of points of action and reaction defined by supports and backrests between tooth and adapter are within the possible geometrical limits of the keying system adopted.
The geometrical positioning accuracy required at the time of first fitting as well as in the event of subsequent adaptation of teeth on adapters demonstrates that interchangeability is difficult to obtain and monitor and, in every case, is very expensive. The shapes obtained in some cases are complex and involve costly manufacturing processes. In addition, fitting is not easy to achieve when it is necessary to change teeth on adapters on site if the tightening of keys is excessive.
According to the prior art, the possibility of placing packing strips made of compressible materials between the tooth and adapter which are therefore no longer in direct contact is also known. This applies, in particular, to U.S. Pat. No. 3,538,156. These strips of compressible material cannot withstand the mechanical stresses transmitted to the tooth, their staying in position is problematic during service when the teeth move and they are gradually damaged.
U.S. Pat. No. 3,707,788 makes provision for placing a deformable predefined elastomer at the bottom of the tooth on which the end of the adapter rests; said material fulfils a backrest function but does not provide a joint between the tooth and the adapter.
The use of a fluid material capable of creating, after cooling, a final imprint to allow fixing of the support shank of the adapter tip on which a tooth is separately mounted and secured by means of fixing is also known from U.S. Pat. No. 4,470,210 ESCO. The only function of this predefined imprint is to allow easy changing of the tooth-adapter assembly and to allow repositioning under defined angular relationship and orientation conditions of a new assembly on the basis of the imprint.
All the documents within the scope of the prior art suggest no simple and quick way of assembling and disassembling a tooth on an adapter which ensures strength of the assembly under all circumstances given stresses during use.